Why can't tartar be removed by brushing no matter how hard you scrub? Calculus is plaque mineralized by calcium/phosphate from saliva — it becomes stone-like, locked onto the tooth surface. Brushing removes soft plaque but can't dissolve mineral. Only professional scaling (ultrasonic/hand instruments) fractures it off. Students learn the prevention moral: remove plaque daily while it's soft, or it becomes tartar that only the dentist can remove.